tests: Allow `objcopy --help` to fail, because it fails on FreeBSD

This is a partial revert of b248f348. Eventually, this commit can be
dropped once `objcopy --help` doesn’t exit with a non-zero status on
FreeBSD.

See: !2360 (comment 1318608)

Signed-off-by: Philip Withnall <pwithnall@endlessos.org>